EFFECTS OF SULFUR CONCENTRATION ON THE PHOTOSYNTHETIC PHYSIOLOGY AND BIOCHEMICAL COMPOSITION OF SCENEDESMUS ACUMINATUS

Scenedesmus acuminatus microalgae are capable of accumulating lipids when exposed to different sulfur concentrations and are therefore considered promising organisms for biodiesel production. Using column photobiorea-ctors, the relevance of different sulfur concentration (2.0S, 1.0S, and 0.25S) on the growth and photosynthetic physiology of the algae was investigated. The initial sulfur concentration had a significant effect on the growth of S. acuminatus (P<0.05). A maximum biomass of 7.47 g/L was obtained in the 2.0S group, which was significantly higher than that of the 1.0S and 0.25S groups (6.43 g/L and 4.17 g/L, respectively; P<0.05), indicating that the addition of sulfur-rich nutrients could promote algae growth. The changes in chlorophyll and band total carotenoid content in S. acuminatus positively correlated with the initial sulfur level in the medium. At the beginning of cultivation, rapid accumulation of carbohydrates occurred under low sulfur conditions; the 0.25S group achieved the highest carbohydrate content accounting for 44.37% of the dry weight, which was 14.43% and 13.78% higher than that of the 1.0S and 2.0S groups, respectively. With a decreased carbohydrate and protein content, lipid content increased significantly in the later stages of cultivation. The 0.25S group acquired the maximum lipid content (55.15% of the dry weight), which was significantly higher than that of the other two groups (P<0.05). Meanwhile, the photosynthetic oxygen evolution rate, maximum light energy conversion efficiency of PSⅡ (F_v/F_m), actual light energy conversion efficiency (yield), and the relative electron transfer efficiency (ETR) positively correlated with the initial sulfur concentration in the culture medium; the whole culture period showed a tendency to increase first and then significantly decrease. The results of fluorescence emission spectroscopy at 77 K showed that there was light energy allocation between the two photosynthetic systems at the cultivation prophase. In conclusion, growth, lipid accumulation, and photosynthetic physiology of S. acuminatus were apparently influenced by the sulfur concentration.